The First World War was an unprecedented catastrophe that killed millions and set the continent of Europe on the path to further calamity two decades later. But it didn’t come out of nowhere.

With the centennial of the outbreak of hostilities coming up in 2014, Erik Sass will be looking back at the lead-up to the war, when seemingly minor moments of friction accumulated until the situation was ready to explode. He'll be covering those events 100 years after they occurred. This is the 17th installment in the series. (See all entries here.)

May 12, 1912: Balkan Bedlam Beckons

While the world focused on Italy’s war with the Turkish Ottoman Empire, an even bigger conflict was brewing in the Balkans, where an international conspiracy against the beleaguered Turks was coming together in the form of the Balkan League. The first step had been taken in March 1912, when Bulgaria and Serbia signed a defensive pact with a secret protocol dividing up the Turkish territory of Macedonia. On May 12, 1912, another Balkan country joined the conspiracy, with the signing of a secret pact between Bulgaria and Greece.

In their “Treaty of Alliance and Defense,” Bulgaria and Greece vowed “not to give this agreement, which is purely one of defense, an aggressive tendency in any way whatsoever,” promising only to assist each other if either party were attacked by the Ottoman Empire. But like the alliance between Serbia and Bulgaria, the partnership between Greece and Bulgaria ended up having little to do with defense and a lot more to do with grabbing territory from the hated Turks: the defensive alliance was just a prelude. In September it would be joined by a secret military convention that committed Greece to provide 120,000 troops and Bulgaria 300,000 troops to a joint war against Turkey. Meanwhile the Greek navy would run interception against the Turkish fleet in the Aegean Sea, thus blocking the Turks from bringing reinforcements to the Balkans from Asia Minor and the Middle East.

Also on May 12, 1912, Bulgaria and Serbia signed a military convention in which both powers agreed to provide at least 200,000 troops (each) to a war with the Ottoman Empire. The military convention would be followed later that month by an agreement between the Bulgarian and Serbian General Staffs, in which they set out detailed plans for the attack on the Ottoman Empire. At the center of the plans was a joint attack forming a pincer movement on Skopje, the capital of Turkish Macedonia; at the same time the Serbians would advance on Turkish territory along the Adriatic Sea in Albania, and the Bulgarians would seize Turkish territory along the Aegean Sea in Thrace. Separately, Bulgaria and Greece later agreed that the Greeks would seize Epirus and possibly some parts of southern Macedonia. The key city of Salonika would be occupied by either the Bulgarians or Greeks – both sides hoped to grab it for themselves.

Indeed, while all the conspirators were eager to carve up Turkish territory in the Balkans, trouble was brewing over the division of the spoils, as Bulgaria and Serbia had never agreed on precise borders for their spheres of interest in Macedonia. To move things along, they sidestepped this issue by agreeing to appoint Russia’s Czar Nicholas II as mediator for their dispute. As the most powerful Slavic state, Russia appeared to be a natural choice to arbitrate conflicts between the smaller Slavic states, but the Russian autocrat would fulfill this responsibility only reluctantly, since it meant he would probably have to alienate one of his two client states in the Balkans. The result was a confused muddle that pushed the Balkan Peninsula -- and Europe -- closer to renewed conflict on a much greater scale in 1914.